# 作业先完成，再完美
# 常用运算符
# SELECT 1 + 1
# SELECT 2 - 1
# SELECT 2 * 2
# SELECT 5 / 3
# SELECT 5 div 3
# SELECT 5 mod 3
# SELECT 1 = 1
# SELECT 1 != 1
# SELECT 1 > 1
# SELECT 1 >= 1   --TRUE
# SELECT 1 < 1
# SELECT 1 <= 1
# SELECT 4 not between 1 and 3
# SELECT name FROM class_1 WHERE name is not NULL
# SELECT gender FROM test WHERE gender = '女' AND id = 4 OR id = 5
# SELECT 1 XOR 1
# 常用函数
# SELECT SUM(money) FROM test
# SELECT AVG(money) FROM test
# SELECT MAX(money) FROM test
# SELECT MIN(money) FROM test
# SELECT COUNT(*) FROM test
# SELECT CHAR_LENGTH("money")
# SELECT FORMAT(4399.1111,2)
# SELECT right("abcdefg      ", 2)
# SELECT trim("abcdefg      ")
